Every day is routine for deployed U.S. troops. They pull duty, maintain their gear, and they go on patrol — day in and day out — until all hell breaks loose and a world of insurgents are trying to kill them.

When that happens, the SAW can effectively blanket an area with up to 120 rounds per minute. That's two 5.56mm bullets slipping from the barrel every second — fed from a 200 round belt — inside a quick-change drum.

U.S. troops call it a "Wall of Steel" that has saved more American lives than they can count.

When it works.

The SAW is flawed: Parts break off, it's hard to clean, it jams, and like all machine guns it overheats to the point of uselessness, and changing the barrel isn't always an option.

But like an old cellphone we keep until the plan renews, the SAW is what U.S. troops have until something better comes along.

The following slides are from a firefight with a U.S. Army unit at Combat Outpost Charkh in Afghanistan, and some infrared shots at an indoor range.

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Like most attacks, this one begins suddenly and the soldier wearing the helmet camera quickly lifts his SAW to fire from behind this wall

Despite being loved for its lethal firepower the SAW is no joy to lug around — it weighs 22 pounds with its 200 round ammo drum attached. "A hell of a lot of weight to move around when the s*** gets thick," one infantryman commented.

A breathless radio call: "We're running out of ammo"

SAW gunners returning from Afghanistan tours told us the links holding the bullets together, and the ammo drums, often don't work properly

Sure enough, back in action, this piece of black plastic flies off and lands on the wall. Troops say clips holding the ammo drums to the weapon constantly break off, and this gunner ducks back down to repair the damage.

Which led one Marine gunner to say: "What will you do with the spare barrel if you overheat it? You can't place it in the barrel bag — it will burn through."

But the heat isn't as much an issue as the jamming. Infantry soldiers are trained to aim and fire, as much as possible, rather than just opening up with a machine gun. Though sometimes it's all they can do to just get a shot off — like this soldier reaching above the wall.

In the SAW's downtime the insurgents have gotten closer, so U.S. troops break out fragmentation grenades

A quick pull of the pin, and four seconds later it detonates, killing everything within 15 feet and wounding all within 45 feet. One former soldier told us: "I couldn't believe how powerful grenades were the first time I used them. Definitely not like the movies."